The invention relates to a medical instrument, particularly a surgical instrument with a displaceable push/pull rod arranged on the proximal end of a hand manipulator for activating remote tool parts on the distal end, wherein a force-limiting device is envisaged for limiting the transmission of force from the hand manipulator onto the remote tool parts via the push/pull rod.
This kind of medical instrument can for example be a needle holder, a gripping-, holding- or preparation tool, scissors or other instrument, in which the push/pull rod can be moved back and forth using manual force via the hand manipulator, in order to move, i.e. to open and close, the remote tool parts which are predominantly open-ended tool parts.
These known medical instruments available in various embodiment configurations have a long hollow cylindrical shaft, onto the distal end of which the remote tool parts are arranged. The hand manipulator with a rigid handle element and a swivelling handle element is arranged on the proximal end of the shaft. To activate the remote tool parts via the hand manipulator, the remote tool parts and the swivelling handle element of the hand manipulator are coupled via the push/pull rod which is located in the hollow cylindrical shaft. In this way it is possible to open and close the remote tool parts by counter-adjusting.
These types of medical instruments are often used during minimally invasive surgery where they are introduced into the patient""s body using trocars. Due to the miniaturisation of the instruments required for minimally invasive surgery, the instruments are more sensitive to pressure since, due to miniaturisation, the individual components can only absorb marginal forces, which for example are brought about by hand pressure upon activating the hand manipulator. In the case of the type of medical instruments mentioned earlier, the swivel handle element of the hand manipulator is designed as a lever, wherein the hinge axis of the two handle elements form the lever axis. The distance from the hinge axis to the point at which the push/pull rod is located on the handle element is considerably shorter than the distance from the hinge axis to the finger hole on the end of this handle element. The transmission ratio is generally around 10:1, that is, the standard closing force of the hand of about 100 N is amplified tenfold due to mechanical leverage, is to around 1,000 N.
When using these medical instruments in practice, in particular the gripping and holding tools, the aim is to generally hold an object, for example a swab or a needle and to place it securely and firmly between the remote tool parts. Strong people can exert a closing force onto the hand manipulator of about 150 N or more, which is then amplified to 1,500 N or more due to mechanical leverage. Frequent use of excess pressure on the remote tool parts can lead to material fatigue or even to the remote tool parts fracturing, whereupon loss of small parts in the operating arena particularly during an operation can lead to the patient getting injured.
In order to avoid undue excess forces being exerted onto the push/pull rod via the hand manipulator and therefore onto the remote tool parts, a force-limiting device is known in the practical field in which the transmission of force between the hand manipulator and the push/pull forces and/or the remote tool parts is limited by a force-limiting device. This type of force-limiting device is known for example from DE 197 31 453-C2. With this known device the push/pull rod is designed as a two-piece component, in which both the push/pull rod sections are connected to one another by way of a force-limiting device. One section of the rod is designed with a casing comprising an internal steepening flat body wedge across the direction of movement of the push/pull rod. The other rod section has a tapered cone with a corresponding flat body wedge of the casing upon being subjected to tensile pressure of the push/pull rod, through which a portion of the closing force generated is absorbed, so that no further undue excess pressure can be exerted onto the remote tool parts.
In accordance with another known embodiment configuration the force-limiting device is designed as a spring assembly on the proximal end of the push/pull rod and which absorbs a portion of the force transmitted onto the push/pull rod via the hand manipulator.
All these state of the art known force-limiting devices have indeed proven themselves in practice, however their construction is very complicated and time consuming and therefore expensive.
Moving on from this the invention is based on the exercise of improving a medical instrument of the above mentioned type so that the force-limiting device is simple and cost effective to construct.
The solution to this exercise according to the invention is characterised by the push/pull rod being designed with spring-like elasticity along the line of displacement and thus creating the force-limiting device.
By configuring the push/pull rod as a spring-like elastic component it is possible to produce a medical instrument with a force-limiting device without additional components for the first time.
In accordance with the first embodiment configuration the push/pull rod is designed with at least sectional undulatory curves to provide the spring-like elasticity. This configuration provides the opportunity for the push/pull rod to elongate itself, preferably reversibly, in the area of the undulatory curve in the event of being subjected to excess tensile pressure.
In order to avoid the push/pull rod from jumping from one side of the inner wall of the hollow cylindrical shaft to the other under tensile pressure, the invention furthermore suggests that the undulatory curves of the individual sections be designed offset on planes from one another, so that the push/pull rod can be guided through the inside of the hollow shaft tube in all directions. It suggests that the each of the sections with individual undulatory curves preferably be designed on planes, offset at 90xc2x0 from one another. This embodiment configuration is simple to manufacture by placing the push/pull rod repeatedly into a press.
The invention further suggests an embodiment configuration in which the semi-curves of the undulatory curves creating the undulating force-limiting device are offset at 90xc2x0 or 135xc2x0 from one another.
The spring-like elasticity of the push/pull rod can in one configuration of the invention be adjusted through its shape and the number of undulatory curves go that it is possible for the force-limiting device to be adapted to the respective necessary and appropriate closing pressure.
A second embodiment configuration of the invention suggests that the push/pull rod be designed with at least sectional turned spiral coils to provide the spring-like elasticity. Along with the creation of the undulatory curves, the spiral coil configuration of the push/pull rod offers the opportunity for the push/pull rod to flexibly elongate itself in the event of excess tensile pressure.
With this embodiment configuration the spring-like elasticity of the push/pull rod is preferably adjusted through the gradient of the turned spiral coil sections, in which the turned spiral coil sections preferably have a large gradient.
Finally the invention suggests that the spring-like elasticity of the push/pull rod can be adjusted by way of the material used for the push/pull rod.
Further, for technical and production reasons as well as for increasing operational safety, it is suggested that the push/pull rod be made of one uniform piece of material and/or with a virtually constant cross section.